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What is multi-core architecture and why you need to understand it

Dhananjay Nene has just written a brilliant article in which he gives a detailed overview of multi-core architectures for computer CPUs – why they came about, how they work, and why you should care. Yesterday, Anand Deshpande, CEO of Persistent Systems, while speaking at the IndicThreads conference on Java Technologies exhorted all programmers to understand multi-core architectures and program to take advantage of the possibilities they provide. Dhananjay’s article is thus very timely for both, junior programmers who wish to understand why Anand was attaching so much importance to this issue, and what they need to do about it, and also for managers in infotech to understand how they need to deal with that issue.

Dhananjay sets the stage with this lovely analogy where he compares the CPU of your computer with superman (Kal-El) and then multi-core is explained thus:

One fine morning Kal’s dad Jor-El knocked on your door and announced that Kal had a built in limitation that he was approaching, and that instead of doubling his productivity every year, he shall start cloning himself once each year (even though they would collectively draw the same salary). Having been used to too much of the good life you immediately exclaimed – “But thats preposterous – One person with twice the standard skill set is far superior to 2 persons with a standard skill set, and many years down the line One person with 64 times the standard skill sets is far far far superior to 64 persons with a standard skill set”. Even as you said this you realised your reason for disappointment and consternation – the collective Kal family was not going to be doing any lesser work than expected but the responsibility of ensuring effective coordination across 64, 128 and 256 Kals now lay upon you the manager, and that you realised was a burden extremely onerous to imagine and even more so to carry. However productive the Kal family was, the weakest link in the productivity was now going to be you the project manager. That in a nutshell is the multicore challenge, and that in a nutshell is the burden that some of your developers shall need to carry in the years to come.

What is to be done? First is to understand which programs are well suited to take advantage of a multi-core architecture, and which ones:

if Kal had been working on one single super complex project, the task of dividing up the activities across his multiple siblings would be very onerous, but if Kal was working on a large number of small projects, it would be very easy to simply distribute the projects across the various Kal’s and the coordination and management effort would be unlikely to increase much.

Dhananjay goes into more detail on this and many other issues, that I am skimming over. For example:

Some environments lend themselves to easier multi threading / processing and some make it tough. Some may not support multi threading at all. So this will constrain some of your choices and the decisions you make. While Java and C and C++ all support multi threading, it is much easier to build multi threaded programs in Java than in C or C++. While Python supports multi threading building processes with more than a handful of threads will run into the GIL issue which will limit any further efficiency improvements by adding more threads. Almost all languages will work with multi processing scenarios.